Echo transmitter and receiver having means to produce stable intermediate frequency despite transmitter frequency drift



Dec. 2, 1958 R. C. SANDERS, JR, ET'AL ECHO TRANSMITTER AND RECEIVERHAVING MEANS T0 PRODUCE STABLE INTERMEDIATE FREQUENCY DESPITETRANSMITTER FREQUENCY DRIFT Original Filed Sept. 23, 1950 C/ACU/TS 1 29I \l 1 46 3 a: 34 3 EL ll 3 40 caA/x/ERTEE Maaum-rw? /5 26 DUPLEX if 25EALAA/CER 32 L 45 A ocnL ig- F; osc/zumm A raw/Aral? GENE/W970i? payer/vC. SA/VDERQJR. mum/"1 R. MEACL'A United States Patent ECHO TRANSMITTERAND RECEIVER HAVING MEANS TO PRODUCE STABLE INTERMEDIATE FREQUENCYDESPITE TRANSMITTER FRE- QUENCY DRIFT Royden C. Sanders, Jr., Nashua, N.H., and William R.

Mercer, Belmont, Mass., assiguors to Raytheon Manufacturing Company,Newton, Mass., a corporation of Delaware Continuation of applicationSerial No. 186,420, September 23, 1950. This application August 9, 1956,Serial No. 603,131

12 Claims. (Cl. 250-13) This is a continuation of our application,Serial No. 186,420, filed September 23, 1950, now abandoned.

This invention relates to electrical circuits of the ultrahigh frequencykind employing hollow-pipe wave guides as energy-conducting elements,and more particularly to the arrangement of wave-guide elements in suchcircuits.

In the use of ultra-high frequency electrical energy in radar and likeapparatus, the hollow wave guide is extensively employed to fulfill manycircuit requirements. Numerous elements have been devised which may bearranged together in groups to provide electrical functions in a desiredsequence. volves such an assembly, wherein a duplex balancer, amodulator and a converter, all constructed of wave guides, are assembledinto a single rigid structure which is then available to be connectedwith a radio frequency generator, an antenna and suitable electroniccircuits to.

provide the R. F. head for a complete radar system. The invention makesuse of a wave-guide four-terminal network of a kind having a mainwave-guide section with two side arms joined thereto in series andparallel, respectively, at a common plane intermediate the ends thereof.Such a network is described in Patent No.

2,445,895, issued July 27, 1948, to W. A. Tyrell, shows an example of itin Fig. 7 and explains the operation in connection with Figs. 1 to 5,inclusive. Tyrrell has called this device a duplex balancer. The deviceshown in Fig. 7 of Tyrrell is also popularly known'as a magic tee, andit will be so referred to herein.

The invention envisions the. employment of a first magic tee as a duplexbalancer having one side arm available for connection to a radiofrequency generator, for example a magnetron, and one of its main armsavailable for connection to an antenna, together with a second magic teeemployed in a modulator circuit and having one of its side armsconnected to the remaining main arm of the first magic tee. A thirdmagic tee is employed in a converter circuit, and side arms of themodulator and converter magic tees are connected directly together. Theremaining side arm of the converter magic tee is connected to theremaining side arm of the first, or duplex balancer, magic tee;

The foregoing arrangement results in an extremely rigid wave-guideconfiguration in which, with a few additional elements, a complete R. F.head for a radar two resulting sidebands are made available to the con-The present invention inverter. The remaining additional element is afilter in the wave guide which connects the modulator and convertermagic tees, and has the function of removing one of the'side bands.There is thus provided to the converter a signal which is mixed with thereceived energy arriving from the antenna to provide a signal at an I.F. frequency which is identical to the frequency of the localoscillator, regardless of variations in the frequency of the R. F.generator.

The foregoing and additional advantages of-the invention will be morereadily appreciated from the following description of a particularembodiment thereof. The description refers to the accompanying drawing,the sole figure of which illustrates the embodiment described.

A first magic tee 10 is employed as a duplex balancer, in accordancewith the definition given by Tyrrell in the aforementioned patent, andhas its shunt side arm 11 available for connection to an R. F.generator, not shown. One main arm 12 is similarly available for COIL-nection to an antenna, not shown. The second main arm 13 of the duplexbalancer is connected to the shunt side arm 14 of a second magic tee 15,which is in a modulator circuit of the kind described and claimed inPatent No. 2,468,237, issued April 26, 1949, to the present applicants.As is described in this earlier patent of the applicants, the main arms16 and 17 of the modulator magic tee 15 have crystals18 and 19,respectively, similarly disposed therein, and a local oscillator signalis furnished in push-pull to the crystals by means of a transformer 20,the secondary winding 21 of which is connected at its ends to similarsides of the crystals and is grounded at its center 22. The remainingsimilar sides of the crystals are likewise grounded to the wave guide atpoints 23 and 24. The local oscillator signal.

is brought to the primary winding 25 of transformer20 via'prirnarywinding terminals 26 and 27. 1

The series side arm 28 of the modulator magic tee 15 is connecteddirectly to the series side arm 29 of the converter magic tee 30. Theshunt side arm 31 of the converter magic tee and series side arm 32 ofthe duplex balancer magic tee are directly connected-together. The

' main arms 33 and 34 of the converter magic tee are also provided withsimilarly arranged crystals 35 and 36, respectively, and like sides ofthese crystals are con-- nected to the ends of the primary winding 37 ofan I, F.

transformer 38, the center 39 ofwhich is grounded. The remaining similarsides of the crystals 35 and 36 are grounded to the wave-guide materialat points 39 and 40, 4

and 13. In order to prevent power from being fed into the third of thethree possible paths, namely, the series side arm 32, the other twopaths must be properly terminated, as is well known. If they are notproperly .terminated, they will reflect energy which, in turn, may

appear in a branch which it is desired no energy should enter.Accordingly, the present wave-guide arrangement preferably containsmatching devices in each magic tee to match each of the sectionsproperly. The matching technique is well known to those skilled in theart.

The principles involved are amply explained in a publication entitledMicrowave Techniques, published by the Navy Department, Bureau of Ships,under the .des-

P atented Dec. 2, 1958 ignation NavShips 900,028, June 15, 1944, pages33 to 36, inclusive. Power from the R. F. generator thus divides equallybetween the path to the antenna and the path to the modulator magic'tee15" and, provided these two arms are properly terminated, very littletransmitter power will be transferred across the magic tee to theconverter, or receiver, crystals 35 and 36. Reflected energy from thetarget, arriving in the antenna line 12 will be divided equally betweenthe converter, or receiver, crystals and the radio frequency generatorline 11, and very little reflected energy will pass into line 13 to themodulator magic tee 15.

The wave-guide arrangement of the present invention is intended for usein radar systems of the continuous wave type, wherein -the radiofrequency generator is operated constantly, either with or withoutmodulation. Such systems are described in chapter of Radar SystemEngineering, vol. 1, of the Massachusetts Institute of TechnologyRadiation Laboratory Series, published by McGraw Hill Book Company,Inc., New York, 1947. The reflected energy has information in it whichindicates the range rate, or the range and the range rate, dependingupon whether or not the radio frequency generator has initially beenmodulated.

An attenuator 45 is included in the Wave guide conmeeting the shunt sidearm 14 of the modulator magic tee 15 with a main arm 13 of the duplexbalancer magic tee 10. This attenuator may be of any of the knownforms,'a large number of which are described in the aforementionedpublication Microwave Techniques on pages 156 ,'to 159, inclusive. Weprefer to use a plug made'of polyiron, which is described on page 157 ofsaid publication. The attenuator serves to terminate the line 13 inwhich it is placed, at the'same time permitting the passage of a verysmall amount of radio frequency generator power 'to the two main arms ofthe modulator magic te'e .15, wherein the local oscillator modulatorcrystals 18 and 19 are mounted. The resistance which these'crystals'pre'sent to thewave guide is varied at the local oscillatorrate by feeding the push-pull output of the local oscillator to them.This varying of the resistance of the crystals modulates the energyreceived in this arm fromthe radio frequency generator, producing twoside bands, one above and one below the'R. F. generator frequency, by anamount equal to the local oscillator frequency. As is explained in theaforementioned earlier patent "of the applicants, essentiallycarrier-suppressed modulation results, and only the two side bandsappear in the series side arm 28-of the modulator magic tee 15.

A side-band filter 46 is included in the wave guide connected betweenthe series side arms 28 and 29 of the modulator andconverter magic tees15 and 30, respectively. This filter may take any form which is suitableto remove one of the aforementioned side bands, while permitting theother to remain substantially unaffected. Filters of wave-guide formwhich are suitable for this use are shown, for example, in Patent No.2,432,093, issued December 9, 1947, to A. G. Fox, who illustrates anadjustable band-pass filter in Fig. of this patent, and band-suppressionfilters in Figs. 19 and 20. The signal which arrives in the convertermagic tee 30 thus consists of only one of the aforementioned side bands,and this signal passes to the main arms 33 and 34 in which the convertercrystals 35 and 36 are mounted. Preferably, the side-band filter 46attenuates the high-frequencyside band and passes the low-frequency sideband to the converter crystals. The low-frequency side band is lower infrequency than the R. F.generator, or transmitted, signal by the localoscillator frequency at any instant and, therefore, becomes the localoscillator signal providing'the proper mixing frequency for an I. F.amplifier which is tuned to the same frequency as the local oscillator.

The-invention will .be more clearly understood if suitable exemplaryfrequencies are considered. Thus, the

'4 R. F. generator may be a 10,000 mc. oscillator, for example amagnetron, while the local oscillator, not shown, may oscillate at therate of 68 mc. per second. The side bands then furnished by themodulator will be 10,068 Inc. and 9,932 mc., per second, respectively.The 10,068 mc. per second signal is filtered out by the filter 46, andthe 9,932 mc. per second signal is furnished to the converter. Thissignal differs by 68 mc. per seccnd from the transmitter frequency of10,000 mc. per second, and, therefore, received energy arriving by wayof the antenna and mixed with it is converted to a 68 mc. per secondsignal, suitable for use in I. F. circuits which are adjusted for thisfrequency.

With this type of R. F. system, no other form of automatic frequencycontrol circuit is required. As long as the output frequency of thelocal oscillator remains constant, the transmitter, or R. F. generatorfrequency can change without having an appreciable effect on the outputof the converter crystals, because the local oscillator 'voltage for theconverter is obtained at any instant by subtracting the output of themodulator local oscillator from the instantaneous transmitter frequency.More particularly, with specific reference to the foregoing frequencysignals, the 68 mc. signal of the modulator local oscillator is at alltimes subtracted from the instantaneous transmitter frequency to providethe converter local oscillator signal, which is thus normally 9,932 mc.per second.

Those skilled in the art will appreciate that many variations of theabove-described embodiment of the invention may be made without theexercise of the invention and within the spirit and scope of the presentinvention. It is, therefore, intended that the claims which follow shallbe limited not by the details of the described embodiment, but only bythe prior art.

What is claimed is:

l. A wave-guide configuration comprising means for couplingelectromagnetic energy to said configuration, a first magic tee, awave-guide modulator including a second magic tee having nonlinearimpedance means in each of its main arms, a wave-guide converterincluding a third magic tee having nonlinear impedance means in each ofits main arms, a connection from a main arm of said first magic tee toone side arm of said second magic tee, a connection from the second sidearm of said second magic tee to a first side arm of said third magictee, and a connection from the second side arm of said third magic teeto a first side arm of said first magic tee.

2. A wave-guide configuration comprising means for couplingelectromagnetic energy to said configuration, a first magic tee, awave-guide modulator including a second magic tee having nonlinearimpedance means in each of its main arms, a wave-guide converterincluding a third magic tee having nonlinear impedance means in each ofits main arms, a connection from a main arm of said first magic tee tothe shuntside arm of said second magic tee, a connection from the seriesside arm of said second magic tee to the series side arm of said thirdmagic tee, and a connection from the shunt side arm of said third magictee to the series side arm of said first magic tee.

3. A wave-guide configuration comprising means for couplingelectromagnetic energy to said configuration, a first magic tee, awave-guide modulator including a second magic tee having similarlyarranged nonlinear impedance means in each of its'main arms, awave-guide converter including a third magic tee having nonlinearimpedance means in each of its main arms, a first connection from a mainarm of said first magic tee to one side arm of said second magic tee, asecond connection from the second side arm of said second magic tee to afirst side arm of said third magic tee, a third connection from thesecond side arm of said third magic tee to a first side arm of saidfirst magic tee, means to provide a modulation signal in push-pull tothe nonlinear impedance means of said wave guide modulator, and means insaid second connection to suppress one of the side bands resulting whena microwave signal introduced into said modulator via said one side armthereof is modulated by said modulation signal.

4. A wave-guide configuration comprising means for couplingelectromagnetic energy to said configuration, a first magic tee, awave-guide modulator including a second magic tee having nonlinearimpedance means in each of its main arms, a wave-guide converterincluding a third magic tee having nonlinear impedance means in each ofits main arms, a first connection from a main arm of said first magictee to one side arm of said second magic tee, a second connection fromthe second side arm of said second magic tee to a first side arm of saidthird magic tee, a third connection from the second side arm of saidthird magic tee to a first side arm of said first magic tee, andattenuator means in series in said first connection.

5. A wave-guide configuration comprising means forcoupling'electromagnetic' energy to said configuration, a first magictee, a wave-guide modulator including a second magic tee havingsimilarly arranged nonlinear im pedance means in each of its main arms,a wave-guide converter including a third magic tee having nonlinearimpedance means in each of its main arms, a first connection from a mainarm of said first magic tee to one side arm of said second magic tee, asecond connection from the second side arm of said second magic tee to afirst side arm of said third magic tee, a third connection fromthe'sec'ond side arm of said third magic tee to'a first side arm of saidfirst magic tee, means to provide a modulation signal in push-pull tothe nonlinear impedance means of said wave-guide modulator, means insaid second connection to suppress one of the side bands resulting whena microwave signal introduced into said modulator via said one side armthereof is modulated by said modulation signal, and attenuator means inseries in said first connection.

6. In combination, a wave-guide configuration comprising means forcoupling electromagnetic energy to said configuration, a first magictee, a wave-guide modulator including a second magic tee havingsimilarly arranged nonlinear impedance means in each of its main arms, awave-guide converter including a third magic tee having nonlinearimpedance means in each of its main arms, a first connection from a mainarm of said first magic tee to one side arm of said second magic tee, asecond connection from the second side arm of said second magic tee to afirst side arm of said third magic tee, a third connection from thesecond side arm of said third magic tee to a first side arm of saidfirst magic tee, means to provide a modulation signal in push-pull tothe nonlinear impedance means of said wave-guide modulator, a source ofmicrowave energy connected to the second side arm of said first magictee, and means in said second connection to suppress one of the sidebands resulting from modulation of said radio frequency energy with saidmodulation signal in said modulator.

7. In combination, a wave-guide configuration comprising means forcoupling electromagnetic energy to said configuration, a first magictee, a wave-guide modulator including a second magic tee havingnonlinear impedance means in each of its main arms, a wave-guideconverter including a third magic tee having nonlinear impedance meansin-each of its main arms, a connection from a main arm of said firstmagic tee to one side arm of said second magic tee, a connection fromthe second side arm of said second magic tee to a first side arm of saidthird magic tee, a connection from the second side arm of said thirdmagic tee to a first side arm of said first magic tee, the second sidearm of said first magic tee being adapted to be connected to asource ofradio frequency energy, means to provide a modulation signal to thenonlinear impedance means of said modulator, and output means 67connected to the nonlinear impedance means of said converter.

8. In a microwave radar system including a source of microwave energy, afirst wave-guide four-terminal network having said source connected toone terminal there of and arranged to divide said energy substantiallyequally between the second and third terminal thereof, said secondterminal being adapted for connection to an antenna, a second wave-guidefour-terminal network having its first terminal connected to the thirdterminal of said first network and arranged to furnish the energyreceived in its first terminal in substantially equal amounts to itssecond and third terminals, first and second nonlinear impedances insaid second network second and third terminals, respectively, means toprovide a modulation signal to said impedances, a third wave-guidefour-terminal network, a connection from the fourth terminal of saidfirst network to the first terminal of said third network, said firstterminal of said third network being arranged to furnish energy receivedtherein to the second and third terminals thereof in substantially equalamounts, third and fourth nonlinear impedances in said second and thirdterminals of said third network, output means connected to said thirdand fourth nonlinear impedances, and a connection from the fourthterminal of said third network to the fourth terminal of said secondnetwork.

9. In a microwave radar system including a source ofmicrowave energy, afirst wave-guide four-terminal network having said source connected toone terminal thereof and arranged to divide said energy substantiallyequally between the'second and third terminals thereof, said secondterminal being adapted for connection to an antenna, a second wave-guidefour-terminal network having its first terminal connected to the thirdterminal of said first network and arranged to furnish the energyreceived in its first terminal in substantially equal amounts to itssecond and third terminals, first and second nonlinear impedances insaid second network second and third terminals, respectively, means toprovide a modulation signal to said impedances, a third wave-guidefour-terminal network, a connection from the fourth terminal of saidfirst network to the first terminal of said third network, said firstterminal of said third network being arranged to furnish energy receivedtherein to the second and third terminals thereof in substantially equalamounts, third and fourth nonlinear impedances in said second and thirdterminals of said third network, output means connected to said thirdand fourth nonlinear impedances, a wave-guide connection from the fourthterminal of said third network to the fourth terminal of said secondnetwork, and means in said wave-guide connection to suppress one of theside bands resulting from modulation of said microwave energy with saidmodulation signal.

10. In a microwave radar system including a source of microwave energy,a first wave-guide four-terminal network having said source connected toone terminal thereof and arranged to divide said energy substantiallyequally between the second and third terminals thereof, said secondterminal being adapted for connection to an antenna, a second wave-guidefour-terminal network having its first terminal connected to the thirdterminal of said first network and arranged to furnish the energyreceived in its first terminal in substantially equal amounts to itssecond and third terminals, attenuator means in the connection betweensaid first and second networks, first and second nonlinear impedances insaid second network second and third terminals, respectively, means toprovide a modulation signal to said impedances, a third waveguidefour-terminal network, a connection from the fourth terminal of saidfirst network to the first terminal of said third network, said firstterminal of said third network being arranged to furnish energy receivedtherein to the second and third terminals thereof in substantially equalamounts, third and fourth nonlinear impedances in said second and thirdterminals of said third network, output means connected to said thirdand fourth nonlinear impedances, and a connection from the fourthterminal of said third network to the fourth terminal of said secondnetwork.

11. In a microwave radar system including a source of microwave energy,a first wave-guide four-terminal network having said source connected toone terminal thereof and arranged to divide said energy substantiallyequally between the second and third terminals thereof, said secondterminal being adapted for connection to an antenna, a second wave-guidefour-terminal network having its first terminal connected to the thirdterminal of said first network and arranged to furnish the energyreceived in its first terminal in substantially equal amounts to itssecond and third terminals, attenuator means in the connection betweensaid first and second networks, first and second nonlinear impedances insaid second network second and third terminals, respectively, means toprovide a modulation signal to said impedances, a third wave-guidefour-terminal network, a connection from the fourth terminal of saidfirst network to the first terminal of said third network, said firstterminal of said third network being arranged to furnish energy receivedtherein to the second and third terminals thereof in substantially equalamounts, third and fourth nonlinear impedances in said second and thirdterminals of said third network, output means connected to said thirdand fourth nonlinear impedances, a wave-guide connection from the fourthterminal of said third network to the fourth terminal of said secondnetwork, and means in said wave-guide 8 connection to suppress one ofthe side bands resulting from modulation of said microwave energy withsaid modulation signal.

12. A wave-guide configuration comprising means for feedingelectromagnetic energy to said configuration, a first wave-guidefour-terminal network having a first terminal and arranged to divideenergy received therein substantially equally between the second andthird terminals thereof, a second wave-guide four-terminal networkhaving its first terminal connected to the third terminal of said firstnetwork and arranged to furnish energy received in its first terminal insubstantially equal amounts to its second and third terminals, first andsecond nonlinear impedances in said second network second and thirdterminals, respectively, a third wave-guide fourterminal network, aconnection from the fourth terminal of said first network to the firstterminal of said third network, said first terminal of said thirdnetwork being arranged to furnish energy received therein to the secondand third terminals thereof in substantially equal amounts, third andfourth nonlinear impedances in said second and third terminals of saidthird network, and a connection from the fourth terminal of said thirdnetwork to the fourth terminal of said second network.

References Cited in the file of this patent UNITED STATES PATENTS

